Actual capacity is not same for lead-acid vs. lithium. You can't run lead-acid down below 50% or else you'll shorten its life-span tremendously. So actual usable capacity is only 1/2 of rating. Lithium
can be run all way down.
Until protection-circuit disconnects it. Here's annoying part is you can't re-connect battery by just pushing button. You have to connect charger to it when hitting reset button to reconnect it. That's to make sure that battery will actually be charged rather than someone just sitting there hitting button constantly and continuing to discharge battery with lights, clocks, etc.
Starter only sucks 40-60a anyway, so either type of battery is more than enough. I made my own lithium battery using 4x18650 LiFePO4 cells. for 0.5lbs.
Kinda like this:
Link to original page on YouTube.
Note that LiFePO4 Lithium-iron is completely different chemistry than Lithium-ion (really lithium-cobalt) that laptops uses. Those are the ones that gets unstable when overly charged or discharged and overheat and cause fires. Lithium-iron is extremely stable and inert chemistry. You can put one on a fire and when casing is melted away, innards of battery will spill and put out fire!